In recent years, non-volatile memories that are data-rewritable semiconductor devices are widely used.
In memory reading, an output current is obtained by applying a word line reference voltage to a gate of the memory cell and applying a bit line voltage to source/drain of the memory cell. Then, the output current is compared with a reference current to determine the bit stored in the memory cell.
In memory, sense amplifiers are used for bit reading. For example, for a memory cell of 256 M, it may require 1K (i.e. 1024) sensing amplifiers for data sensing/reading. For reading a page data for example including 256 bits, 256 sensing amplifiers in a SA circuit (for example having 1K sensing amplifiers) concurrently operate for sensing 256 bits. If the memory cell is larger, more sensing amplifiers may be needed. Thus, the circuit area and the current consumption become important issues. Further, during parallel sensing for multiple bits, the common source level may be raised due to large read current flowing through drain sides and accordingly the read margin for sensing erase cells is reduced and thus undesired.